(a) Field of the Invention
The present invention relates to an organic light emitting device and a driving method thereof. More particularly, the present invention relates to an organic light emitting device having improved screen uniformity, and a driving method thereof.
(b) Description of the Related Art
In general, active flat panel displays respectively include a plurality of pixels arranged in a matrix, and control the light intensity of each pixel on the basis of predetermined luminance information to display images. Among the active flat panel displays, an organic light emitting device is a display in which fluorescent organic materials are electrically excited to display images. The organic light emitting device is self-emissive and has low power consumption, a large reference viewing angle, and a high pixel response speed. Accordingly, the organic light emitting device is suitable for displaying a motion picture at a high definition.
The organic light emitting device includes organic light emitting diodes (“OLEDs”) and thin film transistors (“TFTs”) for controlling the OLEDs. The TFTs are classified as polysilicon TFTs and amorphous silicon TFTs, depending on the type of active layer.
Since the amorphous silicon can be deposited at a low temperature to form a thin film, it can be applied to a display that has a glass substrate having a low melting point. However, amorphous semiconductor has low electron mobility, which hinders a display device from being enlarged. In addition, when the amorphous silicon TFT is continuously supplied with a direct voltage at its control terminal, a threshold voltage of the amorphous silicon TFT is changed which degrades the performance of the TFT and thus, a reduction of the life span of the organic light emitting device may result.
Therefore, it is required to apply a polysilicon TFT having high electron mobility, excellent high frequency operation characteristics, and a low leakage current. Particularly, a low temperature polysilicon (“LTPS”) backplane can remarkably solve the problem of the life span. However, laser shot marks that are made in a laser crystallization process cause deviation of the threshold voltages of driving transistors in a device, thereby causing deterioration in screen uniformity.